1. Field of the Invention
The present invention relates to remote control systems. In particular, the present invention relates to wireless remote control systems that determine control signals based on users' gestures.
2. Description of the Prior Art
Wireless control of electrical/electronic devices, for instance, garage door opening, audio/video equipment (TV) control, air conditioner control, projector control, wireless mouse, and so on, is becoming indispensable. Wireless controllers provide the convenience that saves users from walking to the devices that they want to control. Most commercial wireless controllers at the present time are based on radio-frequency (RF) or infrared signals to communicate the intended commands to the controlled devices.
Practically, besides RF and infrared signals, ultrasonic signals can also be used for remote wireless control purpose. U.S. Pat. No. 4,578,674 discloses a wireless cursor control using a position device (mouse). In this patent, two detectors disposed at the computer side detect how a wireless mouse moves based the ultrasonic signal emitted by the mouse; a cursor on a display panel is accordingly controlled. Because of the Doppler effect, the frequencies detected by the two detectors (represented as f1 and f2) at the computer side are different from the original frequency of the ultrasonic signal emitted by the mouse (represented as f0). The microprocessor at the computer side first calculates the difference between f1 and f0 and the difference between f2 and f0. According to the two differences, the microprocessor estimates the direction and velocity of the mouse motion relative to the detectors. Then the patent calculates the movement of the position device from an initial location and moves the cursor on the display accordingly.
The disadvantage of the above idea is that the calculation is highly related to the reference frequency of the ultrasonic signal emitted by the mouse (f0). More specifically, the calculation cannot be done without knowing the value of f0. Hence, in U.S. Pat. No. 4,578,674, an infrared emitter for providing a reference signal is set at the computer side. Correspondingly, an infrared receiver for receiving the reference signal is set on the position device (mouse). A continuous-wave signal with the exact frequency f0 is carried on an infrared signal through modulation. At the position device, an infrared receiver and a demodulator can recover that signal for generation of the ultrasonic signal with frequency f0. In other words, through this reference signal, the computer side controls the frequency of the ultrasonic signal emitted by the mouse (f0). However, including an infrared receiver at the remote control device increases both its size and power consumption, rendering such control mechanism undesirable.
U.S. Pat. No. 4,654,648 also utilizes acoustic signal emitted from the controller and measure the time difference between signals arriving at several different acoustic receivers. Using triangulation, the patent can determine the position of the controller. This patent does not teach a wireless remote control based on Doppler effect induced from the motion of the controller.
U.S. Pat. No. 5,999,167 teaches another wireless cursor control system based on ultrasonic signal. The ultrasonic signal is emitted from the base unit and the remote controller is equipped with multiple ultrasonic receivers. The phases of the received ultrasonic signals are captured and compared to determine the angular orientation of the remote unit and therefore cursor movement on the display can be accordingly controlled according to the detected orientation change.
U.S. patent application US2007/0115252 is based on U.S. Pat. No. 5,999,167 and includes an extra sensitivity adjuster to extend the application of U.S. Pat. No. 5,999,167 to the cases when the remote controller is at a far distance away from the base unit.
U.S. Pat. No. 6,504,526 presents a wireless pointing device based on infrared signals. Multiple receivers receive infrared pulse-train signal from a transmitter. As the remote unit is moved, the wavefront will arrive at different receivers at different times. By detecting the peaks in the received signal's amplitude (or envelope) and compare their arrival times, movement along a particular direction of the remote control unit can be detected.
In summary, most prior arts use either IR or RF signals for remote control or cursor control. Of those that use ultrasonic signals, most detect the arrival times of the signal or the phases of the signals. Only U.S. Pat. No. 4,578,674 detects the frequencies of the received ultrasonic signals. However, in order to calculate the absolute frequency difference, and thus absolute velocity of the transmitter, U.S. Pat. No. 4,578,674 sends a reference signal with frequency f0 to the remote controller. This requires an extra pair of infrared transmitter and receiver, which necessitates more cost and power consumption.